Rewritable optical recording medium and manufacturing method and apparatus therefor

ABSTRACT

A rewritable optical recording medium includes a segmented groove area in which the groove track is segmented along a rotating direction of the recording medium by groove non-forming portions to form a plurality of groove portions; and a continuous groove area in which a continuous groove is formed, the continuous groove having a groove width smaller than a groove width in the segmented groove area.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a rewritable optical recording mediumand a manufacturing method and apparatus therefor. More particularly,the present invention relates to a rewritable optical recording mediumand manufacturing method and apparatus therefor in which data can berecorded by the user and illegal recording and reproduction of data aredisabled.

2. Description of the Related Art

Optical recording media such as a write-once DVD-R (Digital VersatileDisc—Recordable) and a rewritable DVD-RW (DVD—Re-recordable) are beingput into practical use or under further development. The discs have arecording capacity of a few gigabytes (GB) and data can be recorded bythe user thereon. High-volume data copying can be made with almost noloss of data quality due to the remarkable improvement in performance ofthe large-capacity digital optical recording media as mentioned aboveand a recording and reproducing apparatus.

FIG. 1 is a diagram showing a layout of a physical sector in the radialdirection on the recording surface of a recorded DVD-ROM (DVD—Read OnlyMemory). Information data is recorded in an information area. A lead-inarea, a data area, and a lead-out area are sequentially provided alongthe radial direction from a start point of the information area (i.e.,start point of the physical sector).

The lead-in area includes data for reproduction of the disc such as areference code, control data for configuring a reproduction control datasignal, and the like as shown in FIG. 2. A control data area isconstructed by 192 ECC (Error Correction Code) blocks. In FIG. 2,constructions of the ECC blocks in the control data area are shown byusing relative sector numbers 0 to 15. Each of the contents in those ECCblocks are the same control data. In other words, 192 control data ofthe same contents are sequentially and repetitively recorded. The ECCblock consists of 16 sectors. There is recorded in each ECC blockimportant information regarding copy protection including physicalformat information, disc manufacturing information, and contentsprovider information. The control data regarding reproduction isrecorded into the control data area in the lead-in area when theinformation data is recorded. When the disc is reproduced, thereproducing apparatus reads the data and executes reproduction of therecorded information data such as video data and the like on the basisof the read information.

If the data in the DVD-ROM disc is RF-copied (i.e., a read signal (RFsignal) is recorded as it is by a recording circuit without beingsubjected to signal processing) into the rewritable DVD-RW disc and thecontrol data is illegally falsified, an illegal DVD-RW disc which cannotbe distinguished from the DVD-ROM disc (i.e., an exact or a dead copy ofthe DVD-ROM disc) can be produced. Since a high quality and a largecapacity copy can be easily made by using the DVD-RW disc as mentionedabove, development of a copy protection technique is an importantsubject to prevent a false or illegal copy of the recorded data such asvideo/audio data, a computer program, or the like.

OBJECTS AND SUMMARY OF THE INVENTION

The present invention is made in consideration of the foregoing problemsand it is an object of the present invention to provide a rewritableoptical recording medium which prevents illegal recording andreproduction of information data and manufacturing method and apparatustherefor.

To achieve the object, according to one aspect of the present invention,there is provided a rewritable optical recording medium on which a landtrack and a groove track for recording a data signal are formed, whichcomprises a segmented groove area in which the groove track is segmentedalong a rotating direction of the optical recording medium by groovenon-forming portions to form a plurality of groove portions; and acontinuous groove area in which a continuous groove is formed, thecontinuous groove having a groove width smaller than a groove width inthe segmented groove area.

According to another aspect of the present invention, there is providedA method of manufacturing a master disc for a rewritable opticalrecording medium having a land track and a groove track for recording adata signal by irradiating a laser beam on the master disc, whichcomprises the steps of forming a segmented groove track having aplurality of groove portions in a first area of the optical recordingmedium along a rotating direction of the optical recording medium; andforming, in a second area of the optical recording medium, a continuousgroove track having a groove width smaller than a groove width of thefirst area.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing a layout of a physical sector in the radialdirection of a recording surface of a recorded DVD-ROM;

FIG. 2 is a diagram showing a configuration of a lead-in area and adetailed configuration of a control data area;

FIG. 3 is a perspective view schematically showing a structure of arecording surface of a DVD-RW disc;

FIG. 4 is a diagram showing a detailed configuration of a lead-in areaof a DVD-RW disc;

FIG. 5 is a plan view schematically showing a boundary area of a bufferzone 1 and a control data zone of the DVD-RW disc according to the firstembodiment of the present invention;

FIG. 6 is a graph showing a push-pull signal level against a length ofan extension portion;

FIG. 7 is a graph showing the push-pull signal level against a groovewidth;

FIG. 8 is a graph showing an RF signal level which is caused due tointermittence of groove tracks against the groove width; and

FIG. 9 is a block diagram showing a configuration of a manufacturingapparatus of a master disc of an optical disc.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment of the present invention will now be described in detailhereinbelow with reference to the drawings.

FIG. 3 is a perspective view schematically showing a structure of arecording surface of a conventional DVD-RW disc.

In FIG. 3, an optical disc (DVD-RW) 11 is a phase change type opticaldisc in which information data is rewritable and which has a multilayer15 constructed by a recording layer made of a phase change material (forexample, GeSbTe) serving as a data recording layer and a protectinglayer made of a glass material (ZnS—SiO₂) which sandwiches the recordinglayer. Groove tracks 12 and land tracks 13 are formed thereon. Thegroove tracks 12 serve as information recording tracks and land tracks13 serve as guide tracks for guiding a laser beam (B) on the groovetrack 12 for reproduction or recording. The optical disc also has areflecting layer 16 for reflecting the laser beam (B) when recorded datais reproduced and an adhesive layer 19 for adhering those layers on atransparent substrate (polycarbonate) 18. Further, a transparentsubstrate (polycarbonate) 17 for protecting the layers is provided onthe beam incidence surface of the disc. Prepits 14 corresponding topre-information (i.e., previously recorded information) are formed onthe land track 13. The prepits 14 carry the pre-information which isused by an information recording/reproducing apparatus upon recording orreproduction. The pre-information includes an address information forrecognizing a position on the groove track 12 and sync information. Theprepits 14 are formed prior to shipment of the optical disc 11.

Further, on the optical disc 11, the groove track 12 has been wobbled ata frequency corresponding to a disc rotational speed. The groove tracks12 are wobbled prior to shipment of the optical disc 11. On theconventional optical disc 11, the groove tracks 12 have a predeterminedgroove width and a predetermined groove depth and are formed at apredetermined track pitch.

When recording information data (i.e., information data such as imageinformation to be recorded other than the pre-information) is recordedon the optical disc 11, the wobbling frequency of the groove tracks 12is extracted in the information recording apparatus for controlling theoptical disc 11 to rotate at a predetermined rotational speed. At thesame time, the prepits 14 are preliminarily detected to obtain thepre-information. An optimum output of the laser beam (B) as a recordinglight is determined on the basis of the pre-information. Addressinformation indicating a position on the optical disc 11 where therecording information data should be recorded are obtained on the basisof the pre-information. The recording information data is recorded atthe corresponding recording position on the basis of the addressinformation.

When the recording information data is recorded, the laser beam (B) isirradiated so that the beam center coincides with the center of thegroove track 12 and recording information pits corresponding to therecording information data are formed on the groove track 12. In thisinstance, as shown in FIG. 3, a size of the light spot (SP) is set sothat a part thereof is irradiated not only to the groove track 12 butalso to the land track 13.

The pre-information is detected from the prepits 14 by using a part ofreflection light of the light spot (SP) irradiated on the land track 13by, for example, a push-pull method, so that the pre-information isobtained. The push-pull method (a radial push-pull method) is executedusing a photodetector divided or partitioned by a line that is parallelto the tangential direction of the groove track 12 (i.e., the rotatingdirection of the optical disc 11). Also, a wobble signal is extractedfrom the groove track 12, so that a clock signal for recording which issynchronized with the rotation of the disc is obtained.

The recording information data to be recorded on the optical disc 11 haspreviously been divided every sync frame as an information unit. Onerecording sector is formed by 26 sync frames. One ECC block is formed by16 recording sectors. One sync frame has a length which is 1488 times(1488T) as long as a channel bit length (“T”) that is specified by arecording format at the time when the recording information data isrecorded. Further, a head portion of a length of 32T of one sync frameis used as sync information SY for obtaining synchronization of everysync frame.

The groove track 12 is wobbled at a predetermined wobbling frequency f0(for example, 140 kHz) for all of the sync frames. In the informationrecording/reproducing apparatus, a signal for rotation control of aspindle motor is detected and the clock signal for recording isgenerated by extracting the predetermined wobbling frequency f0.

The first embodiment of the present invention will now be described indetail with reference to FIGS. 4 and 5.

FIG. 4 shows the details of a lead-in area of a DVD-RW disc. Data suchas a reference code, control data, is included in the lead-in area. AnRW-physical format information zone is provided and important controldata for recording/reproduction control of the disc has been written asphase change pits in the zone. In a control data zone locating at thesame address as that of the control data area of the DVD-ROM mentionedabove, in order to inhibit recording and reproduction of the controldata into/from the area, the groove track is formed in a segmentedmanner.

FIG. 5 is a plan view schematically showing a boundary area of thebuffer zone 1 and the control data zone on the DVD-RW disc according tothe first embodiment of the present invention. The control data zone isa segmented groove area 21A (a first area) comprising segmented groovetracks 12A in which a plurality of groove portions 22A are formed in therotating direction of the optical disc 11. In other words, the segmentedgroove track 12A comprises the groove portions 22A and groovenon-forming portions (hereinafter, referred to as mirror portions) 25where no groove is formed. Another area (a second area) such as bufferzone, or data area, etc. is a non-segmented groove area (hereinafter,referred to as a continuous groove area) 21B comprising groove tracks(hereinafter, referred to as continuous groove tracks) 12B in which agroove has been continuously formed (i.e., the groove is not segmented).

In more detail, the segmented groove tracks 12A are alternately arrangedand formed at a predetermined track pitch. The continuous groove tracks12B are also arranged and formed at a predetermined track pitch. Eachgroove portion 22A of the segmented groove track 12A comprises: afundamental pit portion 23 serving as either one of a mark portion or aspace portion; and an extension portion 24 of a groove having apredetermined length. In other words, the extension portion 24 is agroove portion that is appended continuously to the fundamental pitportion 23. The fundamental pit portion 23 carries a mark portion (or aspace portion) while the extension portion 24 and the mirror portion 25(groove non-forming portion) are included in a space portion (or markportion).

The segmented groove track 12A is formed by, for example, a methodwhereby a cutting light beam upon groove cutting is 8/16 modulated andan emitting power is controlled between on and off operation. Moreparticularly, the groove track 12A has an intermittent structuresegmented according to a signal of the same frequency band as that of arecording RF signal (i.e., recording signal obtained after 8/16modulation) which is recorded on the optical disc by the optical discrecording/reproducing apparatus.

Even if the 8/16 modulated control data is recorded on the segmentedgroove track having the above structure, an amplitude of the RF signalreproduced from the segmented groove track 12A is small, so that the RFsignal cannot be read out. This is because the frequency band of the RFsignal that is due to the intermittence (i.e., between ON and OFF) ofthe groove track is equivalent to or comes within that of the recordedRF signal, so that the signals interfere with each other.

In the embodiment, the fundamental pit portion 23 has a pit lengthcorresponding to a mark (or space) of an 8/16 modulation signal S2 in amanufacturing apparatus, which will be explained hereinlater. Forexample, if the 8/16 modulation for converting data of 8 bits into dataof 16 channel bits is used as a modulating method, the minimum pitlength of the fundamental pit portion 23 is equal to 3T and the maximumpit length is equal to 11T (T: channel bit length). For example, themaximum pit length is equal to 14T when a pit having a length 14T isused as a sync pattern.

The extension portion 24 has a length of 3T×0.73 based on an extensionsignal S3, which will be explained hereinlater. A width W1 (in theembodiment, 0.31 μm) of each groove portion 22A on the segmented groovetrack 12A is larger than a groove width W2 (0.26 μm) of the continuousgroove track 12B but is smaller than a half of the track pitch (0.37 μm,the track pitch=0.74 μm).

Description will now be made hereinbelow with regard to how to determineeach groove width and each groove length mentioned above. In theembodiment, the segmented groove track 12A is formed so that the dutyratio of all the fundamental pit portions 23 included in the segmentedgroove track 12A is approximately 50%.

FIG. 6 is a graph showing a photodetection signal level in the push-pullmethod (hereinafter, simply referred to as a push-pull signal level) tothe length of extension portion 24. In the embodiment, the grooveportion 22A is formed by adding the extension portion 24 to thefundamental pit portion 23 to improve the push-pull signal level fortracking control.

As shown in FIG. 6, the push-pull signal level increases as theextension portion 24 becomes longer. Even if the groove track is formedin a segmented manner, the level of the reproduction RF signal increasesby the repetitive recording of the same illegal control data, so thatthe prevention of the recorded data reading becomes imperfect. Theillegal reading can be prevented by shortening the extension portion 24,however, the pushpull signal level decreases as mentioned above and anadverse influence is produced on tracking performance. This trade-offcan be solved by optimizing the groove width of the groove portion 22Ain addition to the length of the extension portion 24.

As shown in FIG. 7, the push-pull signal level changes in accordancewith the groove width. The push-pull signal level reaches a maximumvalue at a value near a half (i.e., 0.37 μm) of the track pitch (0.74μm). Therefore, the groove width should be determined to lie within arange from the groove width (0.26 μn) of the continuous groove track 12Bto a half (i.e., 0.37 μm) of the track pitch (0.74 μm). The length ofextension portion 24 should be determined to have a value such that thesignal level which does not affect the reproducing operation inconsideration of an increased amount of the signal level which iscompensated by the increase of the groove width mentioned above.

FIG. 8 shows the RF signal level due to the intermittence of the groovetrack as a function of the groove width. In this calculation, it isassumed that the fundamental pit portion carries data obtained by the8/16 modulation and the extension portion 24 has a length of 3T×0.73.

The RF signal level that is caused due to the segmented groove trackbecomes a maximum value at a groove width which is slightly smaller thana half (i.e., 0.37 μm) of the track pitch (0.74 μm). To prevent theillegal reproduction, therefore, the groove width of the groove portion22A is determined so as to increase the RF signal level.

Therefore, an optical disc can be provided in which the reduction of thepush-pull signal level can be avoided and the illegal recording andreproduction can be prevented by determining the groove width of thegroove portion 22A, the length of extension portion 24, and the trackpitch as mentioned above.

A duty ratio or the like of the fundamental pit portion 23 can beproperly changed in consideration of the photodetection signal level.

Although the embodiment has been described with respect to the examplein which the extension portion 24 is added to the groove portion 22A, itis not always necessary to provide the extension portion 24. In thisinstance, the groove width and the length of each groove portion can bedetermined in accordance with the duty ratio of the groove portion ofthe segmented groove track in a manner similar to that in the foregoingfirst embodiment.

Although the embodiment has been described with respect to the examplein which the segmented groove track 12A is divided by the signal of thesame band as that of the recording RF signal for the optical disc, itcan also be segmented by a signal including a part of the band of therecording RF signal. Further, the prepits can also be constructed on theland track.

A manufacturing apparatus of a DVD-RW disc according to the secondembodiment of the present invention will now be described in detail withreference to the drawing. FIG. 9 is a block diagram showing aconfiguration of a manufacturing apparatus 30 of a master disc of anoptical disc.

A photoresist 41B is coated on a glass substrate 41A serving as a masterdisc of the DVD-RW disc and patterned through a conventionalphotolithography and etching process.

When the laser beam is irradiated in the control data zone (a firstarea), a dummy control data signal S1 to form the segmented groove track12A is generated in a recording signal generating circuit 31. Thegenerated dummy data signal S1 is 8/16 modulated in an 8/16 modulator32. The extension signal S3 used to extend a mark portion of the 8/16modulation signal S2 by 3T×0.73 is generated in an extension signalgenerating circuit 40. The extension signal S3 is added to themodulation signal S2 in an adding circuit 42 and an addition signal S4is supplied to a power control circuit 33.

A groove width control signal S6 to set the width of groove portion to0.31 μm is supplied from a controller 34 to the power control circuit33. The power control circuit 33 generates a laser power control signalS8 on the basis of the addition signal S4 and a power control signal S7.The power control signal S8 is supplied to an AO (acousto-optic)modulator 38 through an AO driving circuit 39. The AO modulator 38 turnson/off the laser beam from g'i an argon laser 37 on the basis of theaddition signal S4 and adjusts a light power of the laser beam on thebasis of the groove width control signal S6.

When the laser beam is irradiated in an area (a second area) other thanthe control data zone, the control signal S6 for setting the width ofgrooves to 0.26 μm and the control signal S7 to make the laser beam tobe continuously irradiated are supplied from the controller 34 to thepower control circuit 33. The AO modulator 38, therefore, allows thelaser beam emitted from the argon laser 37 to pass through irrespectiveof the addition signal S4 and adjusts the laser beam power on the basisof the groove width control signal S6.

A wobble signal generating circuit 35 generates a wobble signal S9 of asine wave shape to form a wobble to the groove track irrespective of theirradiation area of the laser beam and supplies the signal to afrequency modulator 36. The supplied wobble signal is frequencymodulated by the frequency modulator 36, so that a predeterminedfrequency modulation signal S1 (for example, signal whose centerfrequency is equal to 140 MHz and which changes in a range from 139 MHzto 141 MHz) is generated.

The frequency modulation signal S10 is supplied to the AO modulator 38through the AO driving circuit 39. The AO modulator 38 controls anemitting direction of the laser beam from the argon laser 37 on thebasis of the frequency modulation signal. As mentioned above, since apower of the laser beam which is supplied to the AO modulator 38 iscontrolled by the control signal S8, the photoresist 41B is exposed bythe laser beam from the AO modulator 38, so that it is possible to forma resist pattern for forming the wobbled segmented groove track 12Ahaving the groove width 0.31 μm and the wobbled continuous groove track12B having the groove width 0.26 μm. A master disc for an optical dischaving the segmented groove tracks and the continuous groove tracks canbe formed by etching a master disc glass substrate 41 on which theresist pattern has been formed. The optical recording media mentionedabove can be manufactured by using the master disc.

The numerical values or the like used in the embodiments are shown asexamples and can be properly modified in accordance with the kind ofoptical recording medium, the light source wavelength of the opticalpickup, the optical system, and the like.

As will be obviously understood from the above explanation, according tothe present invention, it is possible to provide the optical recordingmedium and a manufacturing method and apparatus therefor, which canprevent the illegal recording and reproduction of data from the disc.

The invention has been described with reference to the preferredembodiments thereof. It should be understood by those skilled in the artthat a variety of alterations and modifications may be made from theembodiments described above. It is therefore contemplated that theappended claims encompass all such alterations and modifications.

This application is based on a Japanese Patent Application No.2000-205328 which is hereby incorporated by reference.

What is claimed is:
 1. A rewritable optical recording medium having asubstrate, land tracks and groove tracks for recording a data signal,the land tracks and the groove tracks being formed in the substrate, andeach of the groove tracks being positioned between neighboring ones ofthe land tracks, respectively, comprising: a segmented groove area inwhich the groove track is segmented along a rotating direction of saidoptical recording medium to form a plurality of groove portions; and acontinuous groove area in which a continuous groove track is formed,said continuous groove track having a groove width smaller than groovewidths of the plurality of groove portions in said segmented groovearea.
 2. The medium according to claim 1, wherein the groove width insaid segmented groove area is smaller than a half of a groove trackpitch.
 3. The medium according to claim 1, wherein the groove widths ofthe plurality of groove portions in said segmented groove area are basedon a track pitch of the groove track and lengths of the plurality ofgroove portions in said segmented groove area.
 4. The medium accordingto claim 1, wherein the groove portions of the segmented groove area arespaced from each other at intervals, and the intervals are based on apart of a frequency band of a data signal which is recorded on saidoptical recording medium.
 5. The medium according claim 1, wherein saidsegmented groove area is a control data recording area for recording areproduction control data signal.